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BackgroundDue to the prominent particularity of medical work， nurses are prone to developing depression， which not only poses a considerable threat to the physical and mental health of nurses， but also affects the quality of nursing to some extent. Occupational stress is a known contributor to depression in nurses， whereas relatively little research has been done to investigate the underlying mediation path.ObjectiveTo explore the mediation effect of perceived organizational support and psychological capital on the relationship between occupational stress and depression among nurses， and to provide theoretical references for the prevention and treatment of occupational stress-induced depression in nurses.MethodsFrom March to August 2019， a stratified random sampling method was utilized to select a sample size of 720 nurses in each department of a grade A tertiary hospital in Shandong Province. All subjects were assessed using Effort-Reward Imbalance Questionnaire （ERI）， Perceived Organization Support Questionnaire （POS）， Psychological Capital Questionnaire （PCQ） and Center for Epidemiologic Studies Depression Scale （CES-D）. Pearson correlation was adopted to examine the correlation among above scales， and multilevel mediation analyses were conducted with model 6 in Process macro （version 3.3） for SPSS 26.0 using Bootstrap re-sampling method.ResultsA total of 658 nurses （91.39%） completed the effective questionnaire survey. ERI score was positively correlated with CES-D score （r=0.499， P

In order to accurately predict the total organic carbon content of Middle Permian taodonggou group source rocks in Turpan Hami basin, based on the analysis of the relationship between logging parameters of multiple wells and organic matter abundance in the study area, the generalized Δlog R model is extended, that is, a generalized Δlog R model with spontaneous potential is proposed. It is found that the source rock in the study area has a weak positive correlation with resistivity density, a weak negative correlation with spontaneous potential, spontaneous gamma and density, and little correlation with neutrons. Compared with other methods, the correlation coefficient (R2) of the generalized Δlog R model with spontaneous potential is 0.804 2 and the average error rate is 15.58 %, which is the best method to predict the total organic carbon content of the source rocks of the Middle Permian Taodonggou group in the area. The results provide a basis for logging evaluation of source rocks in the study area.

Tight gas is the fastest developing unconventional natural gas resource, becoming the principal part for gas reserves and production growth in China. The Sulige gas field is the largest gas field and also the typical low porosity and low permeability tight sandstone gas field discovered in China, with an annual natural gas output exceeding 300 billion and cumulative output exceeding 290 billion, playing an important role in ensuring national energy provision, helping China’s energy transformation, and promoting green, low-carbon, environmental protection and high-quality development. Based on sample collection and laboratory analysis, natural gas compositions including hydrocarbons, non-hydrocarbons, light hydrocarbons, and noble gases of the Sulige gas field are systematically analyzed, their genetic identifications are identified, and finally gas source originations and contribution proportions are comprehensively discussed from the perspectives of noble gases and hydrocarbon gases. The main achievements are as follows: 1) natural gases in the Sulige gas field are mainly alkane gases, with high methane content, high drying coefficient, low heavy hydrocarbon contents, low non-hydrocarbon gas contents of CO2 and N2, and relatively low noble gas contents. The helium content is relative 2 order of magnitude higher than the atmospheric value, while neon, argon, krypton, and xenon are relatively about 1–2 orders of magnitudes lower than the atmospheric values. 2) The carbon and hydrogen isotopes of alkanes are generally positive sequence distributions with some part inversion. The 3He/4He values are mainly distributed in magnitude of 10−8, the 40Ar/36Ar is ranged from 506 to 1940, the 129Xe is relative loss, and the 132Xe is relative surplus. 3) Natural gases in the Sulige gas field are typical coal-formed gases generated from a humic organic mother material with maturity from high mature to over mature according to C7 and C8 light hydrocarbons and alkane carbon isotopes. Noble gases are typical crustal genesis, mainly originating from the radioactive decay of crustal source materials. 4) The gas source correlations of noble gases and alkane gases and their quantitative evaluations on source contributions show that natural gases in the Sulige gas field are originated from Carboniferous-Permian coal measure source rocks in Ordos Basin, mainly contributed by coals and supplemented by mudstones, accounting for 55–60% and 40–45%, respectively.

U-bimetallic finned tube is a new widely used heat exchange component.In order to predict and control the flowinduced vibration damage of U-bimetallic finned heat exchange tubes,their natural frequencies must be calculated accurately.Inplane and out-of-plane vibration modal of U-bimetallic finned tubes were investigated by means of the hammering method and finite element method.The influence of arc bending radius R of U-bimetallic finned tubes on their natural frequencies was analyzed.The finite element simulation results of natural frequencies of U-bimetallic finned tubes were compared with the measured values for free-free boundary condition,the maximum error of the first 18 order frequencies is 7.3%.The natural frequencies of U-bimetallic finned tubes decrease with increasing the arc radius R for clamped-hinged case.